The use of proteins such as pharmaceutically important proteins, e.g., hormones, and industrially important proteins, e.g., enzymes, has been rapidly growing in recent years. Today, for example, enzymes find frequent use in the starch, dairy, and detergent industries, among others.
In the detergent industry, in particular, enzymes are often configured in a granular form, with an eye toward achieving one or more desirable storage and/or performance characteristics, depending upon the particular application at hand. In these regards, the industry has offered numerous developments in the granulation and coating of enzymes, several of which are exemplified in the following patents and publications:
U.S. Pat. No. 4,106,991 describes an improved formulation of enzyme granules by including within the composition undergoing granulation, finely divided cellulose fibers in an amount of 2-40% w/w based on the dry weight of the whole composition. In addition, this patent describes that waxy substances can be used to coat the particles of the granulate.
U.S. Pat. No. 4,689,297 describes enzyme containing particles which comprise a particulate, water dispersible core which is 150-2,000 microns in its longest dimension, a uniform layer of enzyme around the core particle which amounts to 10%-35% by weight of the weight of the core particle, and a layer of macro-molecular, film-forming, water soluble or dispersible coating agent uniformly surrounding the enzyme layer wherein the combination of enzyme and coating agent is from 25-55% of the weight of the core particle. The core material described in this patent includes clay, a sugar crystal enclosed in layers of corn starch which is coated with a layer of dextrin, agglomerated potato starch, particulate salt, agglomerated trisodium citrate, pan crystallized NaCI flakes, bentonite granules or prills, granules containing bentonite, kaolin and diatomaceous earth or sodium citrate crystals. The film forming material may be a fatty acid ester, an alkoxylated alcohol, a polyvinyl alcohol or an ethoxylated alkylphenol.
U.S. Pat. No. 4,740,469 describes an enzyme granular composition consisting essentially of from 1-35% by weight of an enzyme and from 0.5-30% by weight of a synthetic fibrous material having an average length of from 100-500 micron and a fineness in the range of from 0.05-0.7 denier, with the balance being an extender or filler. The granular composition may further comprise a molten waxy material, such as polyethylene glycol, and optionally a colorant such as titanium dioxide.
U.S. Pat. No. 5,324,649 describes enzyme-containing granules having a core, an enzyme layer and an outer coating layer. The enzyme layer and, optionally, the core and outer coating layer contain a vinyl polymer.
WO 91/09941 describes an enzyme containing preparation whereby at least 50% of the enzymatic activity is present in the preparation as enzyme crystals. The preparation can be either a slurry or a granulate.
WO 97112958 discloses a microgranular enzyme composition. The granules are made by fluid-bed agglomeration which results in granules with numerous carrier or seed particles coated with enzyme and bound together by a binder.
Notwithstanding such developments, there is a continuing need for enzyme granules which have additional beneficial or improved characteristics. For example, while enzyme granules for dry (e.g., powered) detergent formulations have become widely known and extensively developed (as exemplified above), few, if any, granule formulations are available which are suitable for incorporation in liquid detergents.
In some respects, formulators of enzyme granules for liquid detergents must address concerns much like those encountered with dry detergent formulations. It should be appreciated, however, that a liquid-detergent environment presents a variety of challenges of its own. Some of these considerations are discussed next.
In both liquid and dry detergent formulations, enzyme granules should be capable of providing sufficient enzyme activity in the wash. Thus, the enzyme load for each granule needs to be protected from the various harsh components of the liquid formulation (e.g., peroxygen bleaches, such as sodium perborate or sodium percarbonate, and the like).
Another concern, which is common to most all enzyme granules, relates to attrition resistance. In today's state of ever-increasing environmental concern and heightened awareness of industrial hygiene, it is important to keep enzyme dust within acceptable levels. It should be appreciated that human contact with airborne enzyme dust can cause severe allergic reactions. For these reasons, enzyme granule formulators continue their endeavors to control (reduce) the susceptibility of enzyme granules to attritional breakdown.
With particular regard to liquid detergent formulations, one problem with the use of particles (which would include enzyme granules) in liquids is that there is a tendency for such products to phase separate as dispersed insoluble solid particulate material drops from suspension and settles at the bottom of the container holding the liquid detergent product. Phase stabilizers such as thickeners or viscosity control agents can be added to such products to enhance the physical stability thereof. Such materials, however, can add cost and bulk to the product without contributing to the laundering/cleaning performance of such detergent compositions. Further, it is to be noted that the known enzyme granules are generally unsuitable for use in typical liquid detergents as such granules generally have an unacceptably high density (e.g., 1.45 g/cm.sup.3, or higher) which would cause them to drop out of suspension in a relatively short period of time (i.e., much less than the typical product shelf life).
A further problem associated with particles in liquids is that it has been observed that the particles can induce visual inhomogeneities in the final product. This represents a problem, as composition aesthetics is a key element in terms of consumer acceptance.
In view of the above, the development of a low-density, enzyme-containing granule is needed in order to provide cleaning benefit for liquid detergents. The low density is desired so that the particles will stay suspended in the detergent throughout the intended lifecycle of the product. Additionally, it is desired to have the enzymes protected from the harsh detergent environment so that they remain active throughout the product lifecycle.
It is therefore an advantage of the present invention to provide low-density enzyme granules suitable for use in liquid-detergent or cleaner compositions. Preferred granules of the present invention are characterized by one or more of the following desirable features: they have a true density less than 1.4 g/cm.sup.3 ; they exhibit sufficient enzyme activity in the wash; they have relatively low susceptibility to attritional breakdown; they tend to remain dispersed and suspended in the liquid detergent or cleaner during storage and use (e.g., for at least 3 weeks); they provide an acceptable (pleasing) visual appearance.
The production of such a granule exhibiting two or more of the above features has been especially challenging to the industry. For example, the industry is in need of enzyme granules for liquid detergents that have a low density (e.g., less than 1.4 g/cm.sup.3), a low susceptibility to attritional breakdown (e.g., less than 50 mg/pad by Heubach), and retained activity in storage (e.g., greater than 50%). Moreover, an especially desirable granule would additionally disintegrate quickly in the wash liquor to release its enzyme activity. It is an advantage of the present invention to provide granules meeting such specifications.
For some applications, K is desirable to have granules which do not exceed a given size (diameter) specification (e.g., less than 700 micrometers). It is another advantage of the present invention to provide such low-density enzyme granules that are roughly spherical in shape and have a mean diameter of less than 700 micrometers.
It is still a further advantage of the present invention to provide low-density enzyme granules that can be made economically and in commercial quantities. To this end, the present invention provides such granules produced, at least primarily, by way of a fluidized-bed spray coating process.